Electronic ballasts for fluorescent lights typically have highly capacitive input circuits. When switched on, such a ballast draws a large in-rush current to charge up the capacitive load. Manufacturers of electronic ballasts have traditionally included an input filter having an inductor to limit the in-rush current. Recently, however, manufacturers have begun eliminating this input filter, and thus the task of handling the in-rush current has been placed on the switching circuitry used to control the lights.
Air-gap relays have been used to control florescent lighting due to their very high open terminal resistance. However, large in-rush currents may damage relays. When a relay is signaled to close, the internal contacts may bounce several times before ultimately closing. If this relay bounce occurs when switching on a florescent light, the large in-rush current causes arcing to occur each time the relay contacts move apart during a bounce. This arcing can damage the relay contacts. For example, the arcing may cause the contacts to weld to each other. Once welded, the contacts are permanently closed with no way to be reopened. In other cases, the arcing may cause an oxide to form on the contacts. This oxide formation may effectively insulate the contacts such that even when they close, they are still insulated from each other.